Sputtering techniques have been generally applied to a thin film deposition process in the course of fabricating a semiconductor, an LCD (Liquid Crystal Display), a PDP (Plasma Display Panel), a projection TV and the like. The sputtering techniques can be categorized into three types, i.e., an in-line type, a batch type, and an inter-back type, depending on its method of loading and unloading.
In the batch sputtering technique, a substrate is directly loaded into a coating chamber, whereas in the inter-back sputtering technique, a sub-chamber is used. In the in-line sputtering technique, the loading and unloading of the substrate into and from the coating chamber is aided by a loading chamber and an unloading chamber. Further a SiO2 (silica) film and an ITO (Indium Tin Oxide) film are deposited on a surface of the glass substrate in sequence.
A conventional in-line sputtering system includes an entry load-lock module, which changes the interior pressure from atmospheric one to vacuum or vice versa, a buffer heating module for heating the glass substrate, a first sputtering module for depositing a silica film on the glass substrate, a heating module for heating the glass substrate, a second sputtering module for depositing an ITO film on the glass substrate, a buffer cooling module for cooling the glass substrate, and an exit load-lock module, which changes the interior pressure from vacuum to atmospheric one or vice versa.
Each of the modules accommodates a pair of the glass substrates held by a tray. Therefore, a processed substrate must be loaded into the next processing module in sequence before a new substrate can be loaded. While loading the new substrate, the processing condition in the module is disturbed. Hence the processing condition such as pressure needs to be re-adjusted prior to processing the substrate. Only after the processing conditions have been established in the processing module can the processing begin. As a result, under the conventional in-line sputtering system, a continuous sputtering process cannot be achieved.
The re-adjusting process further aggravates the processing outcome, during which time a drastic change in pressure occurs. In particular, when a substrate is loaded into the first sputtering module from the buffer heating module and into the second sputtering module from the heating module, such drastic change in pressure occurs. Respective base pressures of the first and the second sputtering module need to be established lower than those of the buffer heating module and the heating module, respectively, to take account of a rise in pressure when argon gas is supplied therein during the sputtering process. For example, after the substrate is unloaded from the buffer heating module, wherein the interior is maintained at a pressure ranging from 3×10−2 to 5×10−2 Torr, it is loaded into the first sputtering module, at which time it is exposed to the base pressure of approximately 10−6 Torr. Consequently the drastic change in pressure yields high rate of defect. Following the sputtering process, the base pressure rises to the processing pressure of approximately 2×10−3 Torr. The same issue of drastic change in pressure is raised during the second sputtering process, however its detailed description is omitted for the sake of simplicity. The defects that occur on the substrate inevitably affect the quality of silica and the ITO films deposited thereon. Thus the conventional system yields a high rate of defective film deposition.
In the conventional system, the cooling takes place in a single module, specifically in the buffer cooling module. In other words, the processed substrate in the second sputtering module, at approximately 320° C., undergoes forced cooling in the buffer cooling module in a temperature ranging from 100 to 150° C. Consequently, a deterioration of the silica and the ITO films deposited on the substrate occurs due to a high thermal contraction.
Finally, the hinge design of an opening panel in the conventional system does not provide a sufficient amount of workspace while performing maintenance.
Accordingly, development has been pursued for a new in-line sputtering technique capable of providing a continuous and reliable film deposition process to further reduce or eliminate any form of defect due to a large and abrupt change in pressure or temperature.